Certain structures used in aircraft, such as, without limitation, wings, horizontal and vertical stabilizers, fins and the like are often designed to meet or exceed certain design loads. For example, existing metallic wing structures attach a number of discrete, custom manufactured, spanwise stiffeners to thickness tapered skins. The stiffeners and the skin combine at any given buttline cross sectional location to provide at least enough structural material to resist the load on the wing. A maximum number of the stiffeners are used at the wing root where the end load is highest, but the number of stiffeners and/or their thickness is reduced, usually one at a time, going outboard from the root to the tip in order to reduce the structural strength of the wing in a stepwise fashion which roughly matches the continuously reduced loads on the wing from the root to the tip. Skin thickness may also be reduced in a stepwise manner on the outboard portions of the wing. Because the stiffeners and/or the skin are reduced in discrete steps along the length of the wing, the structural strength of the wing may not be closely matched to wing load requirements, thus resulting in overstrength and/or overweight at some locations along the length of the wing.
Adding or deleting discrete stiffeners in order to provide a more exact match between varying structural strength and load requirements may not be feasible in some applications because of the expense of manufacturing and installing the stiffeners, which are relatively complex. Moreover, the use of additional ribs and stiffeners in order to meet load demands may result in weight penalties that reduce cruise efficiency of the aircraft. Finally, existing processes for fabricating wing skins rely on the use of discrete fasteners to attach each stiffener to the wing skin, thereby adding labor and material costs related to drilling precision holes, multiple assembly and disassembly operations and precision fastening operations.
Accordingly, there is a need for structures such as aircraft wings having structural strength that is continuously tailored along their lengths to more precisely match load requirements.